Exciton harvesting, charge transfer, and charge-carrier transport in amorphous-silicon nanopillar/polymer hybrid solar cells

We report on the device physics of nanostructured amorphous-silicon a-Si:H /polymer hybrid solar cells. Using two different polymers, poly 3-hexylthiophene P3HT and poly 2-methoxy-52 -ethyl-hexyloxy -1,4-phenylenevinylene MEH-PPV , we study the exciton diffusion, charge transfer, and charge-carrier transport in bilayer and nanostructured a-Si:H/polymer systems. We find that strong energy transfer occurs in the a-Si:H/MEH-PPV system. However, inefficient hole transfer from the a-Si:H to the polymers renders negligible photocurrent contribution from the a-Si:H as well as very small currents in the a-Si:H/MEH-PPV devices. These results suggest that a-Si:H may be unsuitable for use in polymer-based hybrid cells. Nanosphere lithography and reactive ion etching were used to fabricate nanopillars in a-Si:H. The nanostructured a-Si:H/P3HT devices showed improved efficiency and almost perfect charge-carrier extraction under short-circuit conditions. By modeling these nanostructured devices, the loss mechanisms were identified and solutions for higher efficiencies are suggested. © 2008 American Institute of Physics. DOI: 10.1063/1.2896583